1. Field of the Invention
The present invention relates to a sheet feeding apparatus incorporated into an image forming system such as a printer, copying machine and the like.
2. Related Background Art
In an image forming system such as a printer, copying machine and the like utilizing an ejection tray as a manual sheet supply means, a pair of feed rollers selectively performing operations for feeding a sheet supplied from an upstream side toward a downstream side and for feeding a sheet supplied from the downstream side toward the upstream side are provided as a sheet feeding means. The sheet feeding means normally has guides for directing a leading end of the sheet supplied from the upstream side to a nip between the paired feed rollers.
FIGS. 13 to 15 shows a printer wherein the ejection tray is used as the manual sheet supply means. FIG. 13 shows a condition where a sheet S.sub.1 in a sheet supply cassette 1 is supplied (condition that the sheet S.sub.1 is supplied from the upstream side), FIG. 14 shows a condition where a sheet S.sub.2 is manually supplied from an ejection tray 2 (condition that the sheet S.sub.2 is supplied from the downstream side), and FIG. 15 shows a condition where the sheet S.sub.2 manually supplied from the ejection tray 2 is temporarily stopped on the sheet supply cassette 1.
Within a printer frame 3, substantially at a central portion thereof, there is disposed a print head 7 for printing an image on the sheet S.sub.1 or S.sub.2 by discharging liquid droplets while shifting along guide rails 5, 6. At an upstream side of the print head, there are disposed a pair of feed rollers 9, a convey guide 10, and a sheet supply roller 11 in order. On the other hand, at a downstream side of the print head 7, there are disposed a pair of ejector roller 12.
Further, the sheet supply cassette 1 in which the sheets S.sub.1 are stacked is attached to one side (right side in FIG. 13) of the printer frame 3 (which cassette can be withdrawn in a direction shown by the arrow A in FIG. 13) and the ejection tray 2 is attached to the other side (left side in FIG. 13) of the printer frame.
The pair of feed rollers 9 selectively performs an operation for feeding the sheet S.sub.1 supplied from the upstream sheet supply cassette 1 toward the downstream side and an operation for feeding the sheet S.sub.2 manually supplied from the downstream ejection tray 2 toward the upstream side. When the sheet S.sub.1 supplied from the sheet supply cassette 1 is fed, an upper roller 9a of the paired feed rollers 9 is rotated in a clockwise direction, whereas, a lower roller 9b is rotated in an anti-clockwise direction. On the other hand, when the sheet S.sub.2 manually supplied from the ejection tray is fed, the upper roller 9a of the paired feed rollers 9 is rotated in the anti-clockwise direction, whereas, the lower roller 9b is rotated in the clockwise direction.
The convey guide 10 comprises an upper guide 10a and a lower guide 10b which are secured to the printer frame 3 and which serve to direct a leading end of the sheet S.sub.1 supplied from the sheet supply cassette 1 to a nip between the paired feed rollers 9 (FIG. 13).
A lever 16 (FIG. 14) for detecting the presence/absence of the sheet S.sub.1, S.sub.2 is attached to a smaller diameter portion 15 of the ejector rollers 12 in a sheet passing area. The lever 16 can be rocked around a support shaft 17 in an up-and-down direction and is normally biased by a coil spring 19 so that a trailing end of the lever is pulled downwardly and an arcuate leading end portion 16a is positioned slightly higher than a nip between the paired ejector rollers 12. Accordingly, when the leading end of the sheet S.sub.1 supplied from the sheet supply cassette 1 or the sheet S.sub.2 manually supplied from the ejection tray 2 is pinched by the nip between the paired ejector rollers 12, the arcuate end portion 16a of the lever 16 is lowered around the support shaft 17 in opposition to the coil spring 19. Consequently, a photosensor (not shown) is blocked, thus emitting a sheet presence signal.
A manual sheet supply guide 20 is attached to the ejection tray 2. The guide plate 20 is pivotally mounted on the ejection tray 2 via a support shaft 21. A free end 20a of the guide plate 20 is connected to a plunger 22 (FIG. 14) out of the sheet passing area. When the plunger 22 is turned ON (energized), as shown in FIG. 14, the free end 20a of the guide plate 20 is shifted upwardly to a position confronting to the nip between the paired ejector rollers 12; whereas, when the plunger 22 is turned OFF, the free end 20a of the guide plate 20 is lowered by its own weight to a position in parallel with the ejection tray 2, as shown in FIG. 13.
The printer is provided with a cassette supply mode switch and a manual supply mode switch (both not shown). When the cassette supply mode is selected, the pair of feed rollers 9 take the attitude or posture that they can perform the operation for feeding the sheet S.sub.1 supplied from the sheet supply cassette 1 toward the downstream side, and the pair of ejector rollers 12 take the attitude that they can eject the sheet. In this case, the guide plate 20 on the ejection tray 2 is returned to the condition shown in FIG. 13. On the other hand, when the manual supply mode is selected, the guide plate 20 on the ejection tray 2 is shifted to the condition shown in FIG. 14.
Next, the operations of the printer in the cassette supply mode and in the manual supply mode will be explained.
FIG. 13 shows a condition that the cassette supply mode is selected. When the cassette supply mode switch is turned ON, the sheet supply roller 11 is rotated in a clockwise direction to supply the sheet S.sub.1 from the sheet supply cassette 1. The sheet S.sub.1 is guided by the upper and lower guides 10a, 10b of the convey guide 10 so that the leading end of the sheet is directed to the nip 13 between the feed rollers 9. After the leading end of the sheet S.sub.1 is abutted against the nip 13, the sheet is further conveyed by the sheet supply roller 11 to form a loop in a space within the convey guide 10. Then, the sheet S.sub.1 is fed toward the downstream side by the pair of feed rollers 9, and an image is printed on the sheet by means of the print head 7 in a print area 23. Thereafter, the sheet S.sub.1 is ejected, by the paired ejector rollers 12, onto the ejection tray 2 through an ejection opening 25.
FIG. 14 shows a condition when the manual supply mode is selected. When the sheet S.sub.2 is manually inserted into the printer frame 3 along the lifted guide plate 20, a leading end of the sheet S.sub.2 is abutted against the nip between the ejector rollers 12. Consequently, the arcuate end portion 16a of the lever 16 is pivoted downwardly, whereby the photo-sensor (not shown) emits the sheet presence signal. By this sheet presence signal, the paired ejector rollers 12 and the paired feed rollers 9 are rotated reversely to feed the sheet S.sub.2 manually supplied from the downstream ejection tray 2 toward the upstream side. Accordingly, the sheet S.sub.2 manually inserted from the guide plate 20 is fed toward the upstream side by means of the pair of ejector rollers 12 and then is further fed toward the upstream side by means of the pair of feed rollers 9. When the sheet S.sub.2 passes through the feed roller pair 9, it is introduced between the sheet supply roller 11 and an uppermost sheet in the cassette 1 while being guided by the upper and lower guides 10a, 10b of the convey guide 10, as shown in FIG. 9.
When the sheet S.sub.2 manually supplied from the guide plate 20 of the ejection tray 2 is fed to a position shown in FIG. 15, the sheet is temporarily stopped at that condition. In this condition, the trailing end of the sheet S.sub.2 has passed through the print area 23 and is pinched by the nip 13 of the feed roller pair 9. In order to position the trailing end of the sheet S.sub.2, for example, a count is started after the trailing end of the sheet S.sub.2 has just passed through the lever 16, and, the pair of feed rollers 9 are stopped after a predetermined count.
After the above-mentioned temporary stopping of the sheet S.sub.2, when a sheet supply (print) start signal is emitted, the feed roller pair 9, print head 7 and ejector roller pair 12 are operated in the same manner as the cassette supply mode, and the guide plate 20 is returned to the lowered condition. Accordingly, the sheet S.sub.2 manually supplied is subjected to the printing action in the print area 23 in the same manner as the cassette supply mode, and then is ejected onto the ejection tray 2.
By the way, in the above-mentioned printer, the upper and lower guides 10a, 10b of the convey guide 10 serves to direct the leading end of the sheet S.sub.1 to the nip 13 of the feed roller pair 9 when the feed roller pair 9 feeds the sheet S.sub.1 supplied from the upstream sheet supply cassette 1 toward the downstream side and to direct the sheet S.sub.2 passed through the feed roller pair 9 between the sheet supply roller 11 and the uppermost sheet in the cassette 1 when the feed roller pair 9 feeds the sheet S.sub.2 manually supplied from the downstream ejection tray 2 toward the upstream side.
However, as in the above-mentioned conventional case, when the upper and lower guides 10a, 10b of the convey guide 10 are secured to the printer frame 3 in the vicinity of the nip 13 of the feed roller pair 9, it is feared that the leading end of the manually supplied sheet S.sub.2 is interfered with a free end of the upper guide 10a and/or a free end of the lower guide 19b, thus causing the poor feeding of the sheet. Particularly, it is true when the leading end of the sheet S.sub.2 is curled.
Although this problem can be solved by separating the upper and lower guides 10a, 10b from the nip 13 of the feed roller pair 9, if do so, the upper and lower guides 10a, 10b cannot direct the leading end of the sheet S.sub.2 to the nip 13 of the feed roller pair 9 correctly.